The invention relates to an amplifier for electrical signals and more particularly to a low noise, wideband radio frequency amplifier.
Amplifiers of this type of the known art usually include one or several stages of amplifying components based on transistors or vacuum tubes having passive components such as resistors, capacitors and transformers forming the amplifying circuits. It is well known that all such components introduce a certain amount of electrical noise into the signal to be amplified. There are many types of noises that combine to produce a total noise signal. Sources of noise are the thermal noise produced by any type of resistor, and random noise in semi-conductior amplifiers known as shot noise, or generation-recombination noise produced by fluctuations in free carrier densities when an electric field is applied.
It is well known to use negative feed-back in an amplifier for controlling the amount of noise produced by the amplifier. Negative feed-back includes taking a portion of the output signal and feeding it back to the amplifier input and adjusting its phase so that the feed-back reduces the signal gain through the amplifier. The feed-back circuit can take many forms, depending upon the particular objects sought by the feed-back circuit.